This invention relates to a diesel engine for vehicles that is provided with a mechanism for regulating a flowrate in an intake passage and an exhaust gas recirculation device.
Tokkai Hei 10-288043 published by the Japanese Patent Office in 1998 discloses a diesel engine for vehicles wherein the generation amount of smoke and particulates, and the generation amount of nitrogen oxides xe2x80x94(NOx), are suppressed by maintaining a ratio of an excess air factor and exhaust gas recirculation (EGR) rate of the engine at a constant value.
In a diesel engine provided with a trap for NOx in the exhaust passage, to reduce the NOx accumulated in the trap, it is necessary to reduce the excess air factor to less than one without changing the EGR rate, and supply hydrocarbons (HC) to the exhaust passage as a reducing agent. However, in this control device, it is impossible to vary one of the excess air factor and the EGR rate while keeping the other constant.
Further, the ratio of the excess air factor and EGR rate required to suppress the generation amount of smoke and particulates and the generation amount of nitrogen oxides (NOx), is not necessarily always constant.
It is therefore an object of this invention to make it possible to control the excess air factor and EGR rate independently as required.
It is a further object of this invention to precisely control the excess air factor.
In order to achieve the above objects, this invention provides a control device for such an engine that comprises an intake passage which aspirates fresh air, an adjusting mechanism which varies an aspirating amount of fresh air of the intake passage, an exhaust passage which discharges an exhaust gas of the engine, an exhaust gas recirculation valve which recirculates part of the exhaust gas into the intake passage and a fuel supply mechanism which supplies a fuel to the engine.
The engine burns the fuel with a mixture of fresh air aspirated by the intake passage and exhaust gas recirculated by the exhaust gas recirculation valve.
The control device comprises a sensor which detects a running condition of the engine, a sensor which detects the aspirating amount of the fresh air of the intake passage and a microprocessor. The microprocessor is programmed to determine a target exhaust gas recirculation value of the exhaust gas recirculation valve according to the running condition, control the exhaust gas recirculation valve based on the target exhaust gas recirculation value, calculate a first target value according to the running condition, calculate a second target value based on the first target value and the target exhaust gas recirculation value, control the adjusting mechanism based on the second target value, and control the fuel supply mechanism based on the second target value.
The first target value represents a relation between an amount of air and an amount of the fuel supplied to the engine while
the second target value represents a relation between an amount of the fresh air aspirated by the intake passage and the amount of the fuel supplied to the engine,
This invention also provides a control device for the engine, comprising a mechanism for detecting a running condition of the engine, a mechanism for detecting the aspirating amount of the fresh air of the intake passage, a mechanism for determining a target exhaust gas recirculation value of the exhaust gas recirculation valve according to the running condition, a mechanism for controlling the exhaust gas recirculation valve based on the target exhaust gas recirculation value, a mechanism for calculating a first target value according to the running condition, a mechanism for calculating a second target value based on the first target value and the target exhaust gas recirculation value, and the amount of the fuel supplied to the engine, a mechanism for controlling the adjusting mechanism based on the second target value; and a mechanism for controlling the fuel supply mechanism based on the second target value.
The first target value represents a relation between an amount of air and an amount of the fuel supplied to the engine while
the second target value represents a relation between an amount of the fresh air aspirated by the intake passage and the amount of the fuel supplied to the engine,
This invention also provides a control method for the engine, comprising detecting a running condition of the engine, detecting the aspirating amount of the fresh air of the intake passage, determining a target exhaust gas recirculation value of the exhaust gas recirculation valve according to the running condition, controlling the exhaust gas recirculation valve based on the target exhaust gas recirculation value, calculating a first target value according to the running condition, calculating a second target value based on the first target value and the target exhaust gas recirculation value, controlling the adjusting mechanism based on the second target value, and controlling the fuel supply mechanism based on the second target value.
The first target value represents a relation between an amount of air and an amount of the fuel supplied to the engine while
the second target value represents, a relation between an amount of the fresh air aspirated by the intake passage and the amount of the fuel supplied to the engine,
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.